1. Field of the Invention
This invention relates to a crash energy absorber for a steering shaft, and more particularly to an absorber mounted on the tip end portion of a steering shaft for absorbing a crash energy to protect a driver in case of a accident.
2. Description of the Prior Art
A vehicle steering wheel is mounted on the tip end portion of a steering shaft usually by means of a bolt and nut mechanism. Thus, there is a danger that the driver hit his body at the tip end portion of the steering shaft in case of a crash accident. For the driver's safety it is known that an energy absorbing member is disposed to cover the tip end portion so that the driver may not hit his body at the tip end portion directly and the absorbing member can absorbs the crash energy to relieve the crash shock from the driver. For example, in Japanese Patent Public Disclosure No.58-152660 published on Sept. 10, 1983, there is disclosed a crash energy absorbing structure including a member of U shaped sectional configuration having a top plate covering the tip end of the steering shaft and a pair of parallel side plates extending downwardly from the opposite sides of the top plate perpendicularly to the top plate. The proposed structure is considered as having a desired stiffness against external forces applied thereto in the three different directions, that is, a force in the direction perpendicular to the top plate which is the axial direction of the steering shaft, a force in the direction perpendicular to the axial direction of the steering shaft and parallel with the side plates and a force perpendicular to both the top plate and the side plates so that the crash energy absorbing structure can provide a desirable crash energy absorbing effect for the forces in these three directions. However, the proposed structure is insufficient in stiffness against a diagonally directed force which is applied at a corner portion between the top plate and the side plate so that the energy absorbing structure may deform without showing any absorbing characteristics under such diagonal force. In order to solve the problem, it may be a way to increase the thickness of the member or to provide end plates which are perpendicular to both the top and side plates. However, the solution is not recommendable because the structure becomes too strong against the aforementioned three perpendicular forces.